1. Field of the Invention
The present invention relates to detergent builder compositions comprising a solution of alkali metal silicates enriched in silicon atoms in Q.sub.2 and Q.sub.3 form and inorganic compounds which are inert in respect of such silicates. By the term "builder" is intended any active adjuvant which improves the performance of the surface-active agents in a detergent composition.
These builders are especially useful for formulation in pulverulent detergent compositions, in particular washing powders for a washing machine or dishwasher.
The present invention also relates to detergency cogranulates of alkali metal silicate hydrates and alkali metal carbonates.
2. Description of the Prior Art
By "builder" is intended any active adjuvant which improves the performance of the surface-active agents of a detergent composition.
It is known to this art that such builders must elicit what is designated a "softening" effect on the water employed for washing. It must therefore remove the calcium and magnesium which are present in the water in the form of soluble salts and in the soiling of the laundry (i.e., linen) in more or less soluble complex forms. The removal of calcium and magnesium may be carried out by complexing, in the form of soluble species, or by ion exchange, or by precipitation. If precipitation is involved, this must be controlled to avoid deposition thereof (i.e., incrustations) on the linen or on the components of the washing machines.
This control of precipitation is obtained, in particular, using water-soluble polymers which have an affinity for calcium and magnesium.
The builder must also add to the emulsifying action of the surfactants on fatty soiling, a dispersing action on "pigmentary" soiling such as metal oxides, clays, silica, various dusts, humus, limestone or limescale, soot, and the like.
Such dispersing action is generally attained by virtue of the presence of polyanions, contributing a high density of negative charges at the interfaces.
The builder must also contribute an ionic strength which promotes the activity of the surfactants, in particular by increasing micelle size.
It must also provide OH.sup.- ions for the saponification of the fats and also to increase the negative surface charges on the textile surfaces and particulate soiling.
Silicates have long been considered to be good detergency adjuvants, but are currently less employed in phosphate-free washing machine compositions.
The silicates most widely employed for this application are those which have an SiO.sub.2 /Na.sub.2 O molar ratio ranging from 1.6 to 2.4 or 1.6 to 2.7.
They are marketed either in the form of concentrated solutions at an approximate strength of 35%-45% by weight solids content, or in the form of spray-dried or pulverized and optionally compacted silicate powders.
The concentrated commercial solutions are in most instances prepared from so-called "vitreous", completely amorphous silicate, also known as "soluble glass."
These soluble glasses are rendered water soluble (i.e., hydrosolubilized) in an autoclave under pressure at 140.degree. C. Commercial solutions are thus produced which have a dry solids content of approximately 45% by weight in the case of a silicate of ratio 2 and approximately 35% in the case of a silicate of ratio 3.5.
The concentrated silicate solutions are introduced by the washing powder formulator (detergent manufacturer) into the aqueous suspension (slurry) containing the other constituents of the detergent washing powder. The slurry is then spray-dried. The silicate, spray-dried together with the other constituents, then contains only approximately 25% or 20% of associated water relative to its dry weight, or even less.
As regards the commercial silicate powder, this is produced by spray-drying concentrated solutions of vitreous silicate; 19% or 20% to 22% by weight of water relative to the finished product must be preserved to ensure good solubility of such product.
It has been determined that, when it is dissolved in a washing bath in a proportion of 1 to 3 g/liter, this silicate powder, which contains only 19% or 20% to 22% by weight of associated water (relative to the finished product) exhibits only weak builder properties.
Indeed, this dissolved silicate powder promotes formation essentially of monomeric silicic (silicon containing) species of formula Si(OX).sub.4, where X is H or Na, having no builder activity. Such monomeric species can associate together to form polyanions only if the silicate concentration is at least 50 to 500 g/liter, and do so slowly.
Such silicate concentrations and the slow kinetics of polymerization of the monomeric species are not compatible with the washing conditions and times in a washing machine.
What has been found in the case of a powder containing from 19% or 20% to 22% of bonded (i.e., chemically associated) water (relative to the final product) is, of course, true in the event of formulations containing a silicate with approximately 20% or 25% of associated water (relative to dry silicate) which are prepared by introducing a concentrated silicate solution into a slurry and then drying it.